The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg（-Cu） system. They are widely used in high-performance structural aerospace and transportation applications. Apart from composi...The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg（-Cu） system. They are widely used in high-performance structural aerospace and transportation applications. Apart from compositional, casting and thermo-mechanical processing effects, the balance of properties is also significantly influenced by the way in which the materials are heat-treated. This paper describes the effects of homogenisation, solution treatment, quenching and ageing treatments on the evolution of the microstructure and properties of some important medium to high-strength 7xxx alloys. With a focus on recent work at Monash University, where the whole processing route from homogenisation to final ageing has been studied for thick plate products, it is reported how microstructural features such as dispersoids, coarse constituent particles, fine-scale precipitates, grain structure and grain boundary characteristics can be controlled by heat treatment to achieve improved microstructure-property combinations. In particular, the paper presents methods for dissolving unwanted coarse constituent particles by controlled high- temperature treatments, quench sensitivity evaluations based on a systematic study of continuous cooling precipitation behaviour, and ageing investigations of one-, two- and three-step ageing treatments using experimental and modelling approaches, in each case, the effects on both the microstructure and the resulting properties are discussed.展开更多
Langevin simulations are preformed on the depinning dynamics of fluid monolayer on a quenched substrate. With increase in the strength of the substrate, we find for the first time a crossover from elastic crystal to s...Langevin simulations are preformed on the depinning dynamics of fluid monolayer on a quenched substrate. With increase in the strength of the substrate, we find for the first time a crossover from elastic crystal to smectic flows as well as a crossover from smectic to plastic flows above the depinning. A power-law scaling relationship can be derived between the drift velocity and the driving force for both the elastic crystal and smectic flows, but fails to be obtained for the plastic flow. The power-law exponents are found to be no larger than 1 for the elastic crystal flow and larger than 1 for the smeetic flow. The critical driving force and the averaged intensity of Bragg peaks remain invariant basically in the regime of smectic flow. A sudden increase in the critical driving force is observed within the crossover from the smeetic to plastic flows, and the averaged intensity of Bragg peaks shows sudden decreases within the crossovers both from the elastic crystal to smectic flows and from the smectic to plastic flows. The results are helpful for understanding the slip dynamics of fluids on a molecular level.展开更多
The microstructure of steels treated by Q&P(quenching and partitioning) process was characterized,a method of controlling retained austenite fraction based on inhomogeneous martensitic transformation was proposed,...The microstructure of steels treated by Q&P(quenching and partitioning) process was characterized,a method of controlling retained austenite fraction based on inhomogeneous martensitic transformation was proposed,and the mechanical properties of steels treated by Q&P process were measured.The results show that the microstructure of the studied steels is mainly composed of initial martensite,fresh martensite and retained austenite.The initial marteniste formed at the first quenching step is easily etched;the fresh martensite formed at the final quenching step looks like 'blocky' type phase,and the retained austenite is mainly located on the packet boundary and initial austenite grain boundary.The inhomogeneous microstructure causes the experimental optimum quenching temperature corresponding to maximum retained austenite fraction to be higher than the calculation based on CPE(constrained paraequilibrium) model.The product of tensile strength and total tensile elongation is 47.5 GPa%,and tensile strength of 1760 MPa was obtained for the steel with carbon content of 0.51 wt%.The TRIP(transformation induced plasticity) effects of the large fractioned metastable austenite make a main contribution to the high ductility improvement,and the martensitic matrix provides high strength.展开更多
基金The Aluminium Corporation of China Ltd.(Chalco)for supporting aspects of this work financiallyproviding AA7150 materials as part of the Australia-China International Centre for Light Alloy Research(ICLAR)+1 种基金Monash University for developing the retrogression and reageing Matlab model (as part of the PhD project of Dr Adrian GROSVENOR)The ARC Centre of Excellence for Design in Light Metals and its Directors (first Prof Barry MUDDLE and then Prof Xin-hua WU) for supporting
文摘The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg（-Cu） system. They are widely used in high-performance structural aerospace and transportation applications. Apart from compositional, casting and thermo-mechanical processing effects, the balance of properties is also significantly influenced by the way in which the materials are heat-treated. This paper describes the effects of homogenisation, solution treatment, quenching and ageing treatments on the evolution of the microstructure and properties of some important medium to high-strength 7xxx alloys. With a focus on recent work at Monash University, where the whole processing route from homogenisation to final ageing has been studied for thick plate products, it is reported how microstructural features such as dispersoids, coarse constituent particles, fine-scale precipitates, grain structure and grain boundary characteristics can be controlled by heat treatment to achieve improved microstructure-property combinations. In particular, the paper presents methods for dissolving unwanted coarse constituent particles by controlled high- temperature treatments, quench sensitivity evaluations based on a systematic study of continuous cooling precipitation behaviour, and ageing investigations of one-, two- and three-step ageing treatments using experimental and modelling approaches, in each case, the effects on both the microstructure and the resulting properties are discussed.
基金Supported partially by the Foundation of Henan Educational Committee under Grant No.2008A140011
文摘Langevin simulations are preformed on the depinning dynamics of fluid monolayer on a quenched substrate. With increase in the strength of the substrate, we find for the first time a crossover from elastic crystal to smectic flows as well as a crossover from smectic to plastic flows above the depinning. A power-law scaling relationship can be derived between the drift velocity and the driving force for both the elastic crystal and smectic flows, but fails to be obtained for the plastic flow. The power-law exponents are found to be no larger than 1 for the elastic crystal flow and larger than 1 for the smeetic flow. The critical driving force and the averaged intensity of Bragg peaks remain invariant basically in the regime of smectic flow. A sudden increase in the critical driving force is observed within the crossover from the smeetic to plastic flows, and the averaged intensity of Bragg peaks shows sudden decreases within the crossovers both from the elastic crystal to smectic flows and from the smectic to plastic flows. The results are helpful for understanding the slip dynamics of fluids on a molecular level.
基金supported by a grant from the National Basic Research Program of China (973 Program) (Grant No. 2010CB630803)the Youth Science Funds of China (Grant No. 51101036)
文摘The microstructure of steels treated by Q&P(quenching and partitioning) process was characterized,a method of controlling retained austenite fraction based on inhomogeneous martensitic transformation was proposed,and the mechanical properties of steels treated by Q&P process were measured.The results show that the microstructure of the studied steels is mainly composed of initial martensite,fresh martensite and retained austenite.The initial marteniste formed at the first quenching step is easily etched;the fresh martensite formed at the final quenching step looks like 'blocky' type phase,and the retained austenite is mainly located on the packet boundary and initial austenite grain boundary.The inhomogeneous microstructure causes the experimental optimum quenching temperature corresponding to maximum retained austenite fraction to be higher than the calculation based on CPE(constrained paraequilibrium) model.The product of tensile strength and total tensile elongation is 47.5 GPa%,and tensile strength of 1760 MPa was obtained for the steel with carbon content of 0.51 wt%.The TRIP(transformation induced plasticity) effects of the large fractioned metastable austenite make a main contribution to the high ductility improvement,and the martensitic matrix provides high strength.
